The invention relates to a method for ink supply to ink trays in printing presses. The printing press has an ink tray for ink supply. The tray is adjoined by an ink ball cooperating with ink dosing elements, so that ink zones are established for the varying ink supply to the printing matter and the ink consumption is determined for the ink zones or ink zone groups. The data are inputted to and processed in a computer to produce appropriate control signals for local ink consumption at the particular ink zones or ink zone groups, and an ink supply device traverse parallel to the ink ball, thus supplying the ink requiring ink zones or ink zone groups.
The invention also relates to an apparatus in printing presses for ink supply to ink trays by establishing an ink dosing gap between an adjoining ink ball that extends over the entire width and an ink blade that is separated into multiple ink zones. This apparatus also incorporates an ink supply device controlled by a computer for adjusting ink consumption and the ink supply to the ink zones.
An apparatus to establish a constant ink level in ink trays of printing presses is known, for example from German patent No. 2,324,452 C2. The constant ink level is adjusted to keep a low printing ink volume in the ink tray. An ink agitator is used for this purpose, traversing along the ink ball. The traversing movement of the agitator creates a wave, which is sensed by a sensor travelling above the ink agitator as a gauge for the ink level. The ink supply is stopped if the ink level is exceeding a preset level. This solution is supposed to guarantee a constant low ink level in the ink tray, but it is not possible to supply the ink to particular ink zones according to the inking requirements.
This problem is supposedly solved with German patent No. 19,512,727 A1 with an ink cartridge that is movable on a slide. A traveling sensor is allocated in the direction of motion before the ink cartridge to detect the ink level in the ink zones. The sensor sends a control signal if the ink level is too low. This causes the release of an appropriate ink volume from the ink cartridge. This solution has the disadvantage that the ink tray cannot be properly emptied at the end of a job. The ink supply takes place according to demand, therefore an uneven surface profile develops with areas of ink accumulation at job end in those areas that have low ink consumption. These ink accumulations cannot be any longer used for printing, and remains in the ink tray of the printing press.
Another device for supplying printing ink is known from German patent No. 4,424,591 C1. A pre-set counter set for the job size is used to empty the ink tray at the end of the job. The pre-set counter is within a circuit with the ink supply. Therefore, the ink supply can be stopped through the ink supply device, by a control signal before the end of the job depending on the number of already printed products. This device also does not enable emptying the ink tray without any residues, due to the uneven surface profile.
It is an object of the present invention to provide a method and an apparatus for zonal ink dosage according to the ink requirements with an emptied ink tray at the end of the job or at job change, which is free of extensive residue.
The object is achieved according the present invention by stopping the ink supply before the end of the printing job. This point is determined so that a minimum amount of ink remains in the ink tray at the pre-determined end point of the job that is sufficient to process the required product volume and the ink is shifted from ink zones or ink zone groups with lesser degree of ink consumption to ink zones or ink zone groups with momentarily higher ink consumption for processing and completing the remaining printing job.
The advantage of the solution according to the present invention results in an almost emptied ink tray at the end of the job or at job change. This saves ink and time for manually emptying the ink tray by a pressman.